An inertia drift is the type of drift you do through an S-turn. You drift through the first turn, then use the inertia of that first drift to make the car slide into the second turn.A feint drift is simply turning the opposite direction on a straight, then turning the car in the proper direction.

So basically, it is an inertia drift if you continue a drift from one corner to another. A feint drift is not an inertia drift, because you are starting the drift instead of continuing a drift.

The typical situation for an inertia drift is sliding into an S-turn with a lot of speed. Imagine a rally car on a snowy S-turn. It has to slide to go fast on snow, so it will drift into the turn. Then it has to quickly change direction in the middle of the S-turn to stay on the road, so it will use an inertia drift.For an example of a feint, imagine the rally car on a very short straight before a corner. It is on the inside line, and it has to switch to the outside line to enter the corner with speed. To do this, it moves to the outside of the straight just before the corner, then quickly turns around to slide into it.

The exact technique for inertia drifting and feint drifting changes a little depending on things like speed, car setup and power output, so I do not think I can explain it in a simple way. The simplest I can say for inertia drifting is that you use precise countersteer to change direction as smoothly as possible. If you countersteer more than needed, the car will change direction too quickly and lose speed or spin out.A basic feint drift is steering one way then quickly steering the other way to unsettle the car's weight, and precise steering is also needed to control the car after the flick. There are more advanced feint drift techniques that change the car's direction while also braking the car from high speeds, but you can only understand them when you have a good understanding of car control.

Do note however that, as Xiao said, they're at their most basic the same thing. Whether it's the Scandinavian Flick, an "inertia drift" or a "feint drift" the idea is to use your vehicle's inertia to set up for and carry out a drift maneuver as opposed to, say, relying on braking alone to force your vehicle to oversteer.

I'm personally of the opinion that these are just arbitrary names for the same thing done at different moments, arbitrarily decided by folks who watched too much Anime.